Doctor Eggman attacks a city, and Sonic sets out to stop him. However, upon arriving, he is attacked by Infinite, a mercenary transformed by the power of the Phantom Ruby from Sonic Mania. Infinite defeats Sonic, and he is taken prisoner aboard the Death Egg. Without Sonic, the land is left without a defender, and Eggman, with the help of his robots, Infinite, Shadow the Hedgehog, Chaos, Zavok, and Metal Sonic, manages to conquer the world within six months. Frustrated, Knuckles the Echidna forms a resistance force with Tails, the Chaotix, Amy Rose, Silver the Hedgehog, Rouge the Bat and a survivor of Eggman’s attack whom they nickname the Rookie. Knuckles discovers Sonic’s whereabouts, and the Rookie steals a space shuttle, breaks into the Death Egg, and rescues Sonic. Back in the city, Tails is attacked by Chaos, but is saved by Classic Sonic (also from Sonic Mania). The two set out to spy on Eggman, learning of the Phantom Ruby and that Eggman has a plan to completely destroy the Resistance which will take effect in three days.